Patent Grant
8811882
1. Field of the Invention
The present invention relates to an image forming apparatus using electrophotography, for example, a copying machine or a printer.
2. Description of the Related Art
In inkjet printers, so-called marginless printing is adopted popularly. In marginless printing, a transfer material, such as paper, which does not have a margin on its periphery is used, and an image is formed over the entire transfer material. In LBPs and so on using electrophotography, there is also an increasing demand for marginless printing. For example, Japanese Patent Laid-Open No. 2004-45457 proposes an image forming apparatus capable of marginless printing. In this image forming apparatus, a toner image larger than a transfer material is formed on an image bearing member, and part of the toner image is transferred onto the transfer material, thus achieving marginless printing.
When a toner image on an image bearing member, such as an intermediate transfer member, is transferred onto a transfer material, part of the toner image to be transferred is sometimes scraped off by a leading edge of the transfer material. In this case, the toner image that has been partly scraped off by the leading edge of the transfer material is transferred onto the transfer material. This phenomenon causes defective image forming near the leading edge of the transfer material. Here, defective image forming refers to soiling of the back side of the transfer material with toner, soiling of a leading end face of the transfer material with toner, or density unevenness at the leading edge of the transfer material.
When a margin is formed on the periphery of the transfer material, a toner image is not formed in a region on the image bearing member corresponding to the margin, and therefore, defective image forming rarely occurs.
In contrast, in marginless printing, since a toner image is formed over the entire transfer material, defective image forming occurs quite frequently. Further, although a toner image should be formed to the edges of the transfer material in marginless printing, part of the toner image near the edge is scraped off. Thus, defective image forming is more obvious in marginless printing.
The present invention prevents a phenomenon in which, during marginless printing for forming a toner image to edges of a transfer material, a toner image formed on an image bearing member so as to be transferred onto the transfer material is scraped by a leading edge of the transfer material.
An image forming apparatus according to an aspect of the present invention includes a rotatable image bearing member configured to bear a toner image; a transfer member configured to form a nip portion between the transfer member and the image bearing member; a guide member configured to guide a transfer material to an outer surface of the image bearing member on an upstream side of the nip portion in a rotating direction of the image bearing member; a conveying roller configured to convey the transfer material to the guide member; and a control device configured to control a speed of the conveying roller. The toner image on the image bearing member is transferred onto the transfer material in the nip portion by the transfer member. The image forming apparatus has a marginless print mode in which the toner image is formed on the image bearing member to a region on the image bearing member corresponding to a region outside the transfer material so as to be formed to an edge of the transfer material. When the toner image is formed at least at a leading edge of the transfer material in a conveying direction in the marginless print mode, the control device controls the speed of the conveying roller so that a speed of the transfer material when the leading edge of the transfer material comes into contact with the image bearing member is lower than a rotation speed of the image bearing member.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. The dimensions, materials, shapes, and relative positions of the structural components described in the following exemplary embodiments are to be appropriately modified in accordance with the structure and various conditions of the apparatus to which the present invention is applied. Therefore, the following exemplary embodiments are not intended to limit the scope of the present invention, unless otherwise specified.
The photosensitive drums 1Y, 1M, 1C, and 1Bk are rotated by driving devices (not shown) at a predetermined speed in the directions of the arrows in
The endless intermediate transfer belt 2 is rotated at a speed of 117 mm per second in the direction of the arrow while being stretched by the driving roller 3, the tension roller 4, and the opposing roller for secondary-transfer 5. The intermediate transfer belt 2 is formed of an electron conductive polyimide whose resistance is adjusted by carbon black. The intermediate transfer belt 2 has an electric resistivity of 1×108 Ω·cm, a thickness of 75 μm, an inner perimeter of 1116 mm, and a width of 350 mm in the longitudinal direction (direction orthogonal to the moving direction). The secondary transfer roller 11 is provided with a roller cleaning device 16 that removes and recovers toner remaining on the secondary transfer roller 11 after secondary transfer. The registration rollers 13 have a diameter of 17.4 mm. A surface of one of the rollers in contact with a front side (a side where transfer is performed) of the transfer material P is formed of resin having a surface roughness Ra of 6.3, and a surface of the other roller in contact with the back side of the transfer material P is formed of rubber having a frictional coefficient μ of 0.6. The registration rollers 13 are rotated in the directions of the arrows by a registration-roller driving unit 17. The driving speed of the driving unit 17 is controlled by a driving-speed control device 18. In other words, the speed of the conveying rollers is controlled by the driving-speed control device 18. Guides 15 before secondary transfer regulate the conveying path and attitude of the transfer material P so that the leading edge of the transfer material P enters the secondary transfer region after contacting the intermediate transfer belt 2, thus preventing defective image forming called “scattering” that will be described in detail below.
An image forming operation will now be described. When an image formation starting signal is issued, transfer materials P are fed out one by one, and conveyed to the registration rollers 13. In this case, the registration rollers 13 are stopped, and a leading edge of a conveyed transfer material P stands by just before the secondary transfer region. Subsequently, the registration rollers 13 start to rotate in synchronization with the start of image formation in the image forming stations including the photosensitive drums 1Y, 1M, 1C, and 1Bk, so that the transfer material P is conveyed to the secondary transfer region. In the image forming stations, when an image formation starting signal is issued, formation of toner images corresponding to the colors is started. Since image formation is performed through a similar procedure in the image forming stations, a description will be given of an image forming procedure performed in the image forming station including the photosensitive drum 1Y.
The photosensitive drum 1Y is uniformly charged at predetermined polarity and potential by the charging roller 6Y. Subsequently, an electrostatic latent image corresponding to a yellow color component image is formed on the photosensitive drum 1Y by the exposure device 7Y. Yellow toner adheres to the electrostatic latent image in the developing device 8Y, so that the electrostatic latent image is developed as a visible toner image. The toner image formed on the photosensitive drum 1Y is then transferred onto the intermediate transfer belt 2 in a primary transfer region by the primary transfer roller 10Y to which a primary transfer bias is applied. In this way, color toner images are sequentially transferred from the photosensitive drums 1Y, 1M, 1C, and 1Bk onto the intermediate transfer belt 2 through these processes, thus forming a full color toner image. In this case, toner remaining on the photosensitive drums 1Y, 1M, 1C, and 1Bk is removed and recovered by the drum cleaning devices 9Y, 9M, 9C, and 9Bk.
The full color toner image formed on the intermediate transfer belt 2 is conveyed to the secondary transfer region by the intermediate transfer belt 2. In this case, the transfer material P is conveyed by the registration rollers 13 so as to reach the secondary transfer region immediately before the full color toner image reaches the secondary transfer region. The conveying speed of the transfer material P is substantially equal to the rotation speed of the intermediate transfer belt 2. In the secondary transfer region, the full color toner image is transferred from the intermediate transfer belt 2 onto the transfer material P by the secondary transfer roller 11 (transfer member). Toner that is not transferred, but remains on the intermediate transfer belt 2 is removed and recovered by the belt cleaning device 12. Then, the transfer material P on which the full color toner image is formed is conveyed to the fixing device 14, where it is fixed.
The above-described term “scattering” refers to a phenomenon in which the position to which a toner image is transferred in secondary transfer is unstable. This phenomenon occurs because toner influenced by the voltage applied to the secondary transfer roller 11 is transferred via an air gap on the upstream side of the secondary transfer nip portion.
Marginless printing will now be described. The image forming apparatus of the first embodiment has a print mode for printing an image on a transfer material P having margins on the entire outer periphery, and a marginless print mode for printing an image to edges of a transfer material that includes at least one side having no margin.
In this case, since the size of the toner image is larger than the size of the transfer material P, the toner image on the intermediate transfer belt 2 comes into the secondary transfer region earlier than the transfer material P. Therefore, when the leading edge of the transfer material P comes into the secondary transfer region, it rubs against the intermediate transfer belt 2. This may disturb the toner image on the intermediate transfer belt 2, and may cause defective image forming. Rubbing and prevention thereof will be described below. In the secondary transfer region, the toner image having a size Iv×Ih is transferred onto the transfer material P. Thus, a toner image portion shaped like a frame, as shown in
The reason for rubbing will now be described in detail. In the following description, a time when the leading edge of the transfer material P comes into contact with the intermediate transfer belt 2 is designated as T1 and a time when the leading edge of the transfer material P comes into the secondary transfer region is designated as T2. Further, a moving speed of the surface of the intermediate transfer belt 2 is designated as Vp and a speed at which the transfer material P is conveyed by the registration rollers 13 is designated as Vs.
In
In actuality, however, since the transfer material P has rigidity, it is bent in a curve and is conveyed such that the leading edge thereof moves along the intermediate transfer belt 2, as shown in
One conceivable cause for the above is that the force of the leading edge of the transfer material P, which obliquely contacts the intermediate transfer belt 2, acting toward the intermediate transfer belt 2 is regulated by the intermediate transfer belt 2. Since the force is regulated by the intermediate transfer belt 2, more force toward the secondary transfer region acts on the leading edge of the transfer material P. It is considered that this force and the rigidity of the transfer material P make the moving distance of the leading edge of the transfer material P on the intermediate transfer belt 2 longer than the moving distance of the surface of the intermediate transfer belt 2.
Accordingly, in the first embodiment, the speed Vs is controlled by the driving-speed control device 18 so as to prevent rubbing. When Vp=Vs, as in the image forming apparatus of the related art, L1′>Vp×Δt and rubbing occurs, as described above. Thus, L1′ is reduced in the first embodiment. Since L1′ can be reduced by decreasing Vs, Vs is made lower than Vp from the time T1 to the time T2. On the other hand, when L1′<Vp×Δt by decreasing Vs, rubbing occurs in the opposite direction. Therefore, it is preferable to set Vs so that L1′ is substantially equal to Vp×Δt.
A description will now be given of how to control Vs in the first embodiment.
First, the driving-speed control device 18 controls the driving unit 17 to control the speed of the registration rollers 13 so that Vs at the time T1 becomes about 85% of Vp (about 99.5 mm/sec). In this case, the time T1 is determined on the basis of the time counted from the time when the registration rollers 13 start to convey the transfer material P. Subsequently, the driving-speed control device 18 controls the driving unit 17 so that Vs monotonously increases from the time T1 to the time T2, and becomes substantially equal to Vp at the time T2. After the time T2, the driving-speed control device 18 controls the driving unit 17 so that Vs is kept substantially equal to Vp (about 117 mm/sec). The time T2 is determined on the basis of time counting similar to the time T1.
After the time T2, secondary transfer from the intermediate transfer belt 2 onto the transfer material P is started at the secondary transfer nip portion. Since the toner image to be transferred onto the transfer material P is contracted when Vs<Vp, Vs and Vp are made equal. As described above, rubbing is prevented by controlling the conveying speed of the transfer material P.
In this way, in the first embodiment, the toner image is transferred onto the transfer material P without causing defective image forming even in marginless printing. As described above, the first embodiment can prevent rubbing of the leading edge of the transfer material P against the intermediate transfer belt 2 in marginless printing, and can obtain a print image without causing defective image forming at the leading edge of the transfer material P. Moreover, defective image forming due to rubbing can be prevented without greatly changing the configuration from that of the image forming apparatus of the related art.
While the secondary transfer member is shaped like a roller in the first embodiment, similar advantages can be obtained, regardless of the shape of the secondary transfer member, as long as a difference is formed between the speed of the leading edge of the transfer material and the speed of the intermediate transfer belt 2 on the upstream side of the secondary transfer region.
A configuration and an image forming operation of an image forming apparatus according to a second embodiment are substantially identical to those adopted in the image forming apparatus of the first embodiment. Therefore, components having functions similar to those in the image forming apparatus of the first embodiment are denoted by the same reference numerals, and descriptions thereof are omitted. In the following, structures different from those in the image forming apparatus of the first embodiment will be described chiefly.
A driving-speed control device 18 controls a driving unit 17 so that Vs at a time T1 becomes about 85% of Vp (about 99.5 mm/sec). The time T1 is determined on the basis of time counting similar to that adopted in the first embodiment. Subsequently, the driving-speed control device 18 controls the driving unit 17 to control the speed of registration rollers 13 so that Vs increases from the time T1 to a time T2. In this case, when a midpoint between T1 and T2 is set at T3, the driving unit 17 is controlled so that the amount of increase in Vs from T1 to T3 is larger than the amount of increase in Vs from T3 to T2. After the time T2, the driving-speed control device 18 controls the driving unit 17 so that Vs is equal to Vp (about 117 mm/sec). The time T2 is determined on the basis of time counting similar to that adopted in the first embodiment.
A description will now be given of the control over the conveying speed of the transfer material P from the time T1 to the time T2 in
Δt·Vt2+(2b/Vp)V−Δt+(2b/Vp)cos θ=0
Similarly, (Vs/Vp)×100=V. Therefore, it is considered that rubbing can be prevented by changing V from the time T1 to the time T2, as shown in
As a result of verification of the advantages of the second embodiment using an actual image forming apparatus, rubbing was not visually detected, and the advantages of the second embodiment could be proved. During verification, the rotation speed of the registration rollers 13 was changed every 2 msec in order to control the conveying speed of the transfer material P in a manner similar to the equation. In actuality, the advantages of the second embodiment were observed while changing Vs stepwise at a small interval. This verification proved that rubbing could be prevented by controlling Vs according to the equation. However, not only the equation, but also the following two points are important in the second embodiment.
The first point is to control Vs so that Vs increases with time from the time T1 to the time T2. The second point is to perform control so that the amount of increase in Vs from the time T1 to the time T3 serving as the midpoint between T1 and T2 is larger than the amount of increase in Vs from the time T3 to the time T2. When Vt3 represents the speed of the transfer material the time T3 ((T1+T2)/2), Vt2>Vt3>(Vt1+Vt2)/2.
Because of the above two points, rubbing can be more effectively prevented than in the first embodiment. While the secondary transfer member in the image forming apparatus of the second embodiment is shaped like a roller, similar advantages can be obtained, regardless of the shape of the secondary transfer member, as long as a difference is formed between the speed of the leading edge of the transfer material and the speed of the intermediate transfer belt 2 on the upstream side of the secondary transfer region, in a manner similar to that adopted in the first embodiment.
A configuration and an image forming operation of an image forming apparatus according to a third embodiment are substantially identical to those adopted in the image forming apparatus of the first embodiment. Therefore, components having functions similar to those in the image forming apparatus of the first embodiment are denoted by the same reference numerals, and descriptions thereof are omitted. In the following, structures different from those in the image forming apparatus of the first embodiment will be described chiefly.
To prevent rubbing, it is necessary to control Vs after the time T1. On the other hand, Vs before the time T1 is arbitrary to some extent. Accordingly, in the third embodiment, the conveying speed Vs of the transfer material P before the leading edge of the transfer material comes into contact with the image bearing member is increased, and the same control as in the first or second embodiment is exerted over Vs after the time T1. As a result, the time from when the registration rollers 13 start to convey the transfer material P to when the leading edge of the transfer material P comes into contact with the intermediate transfer belt 2 is shorter than in the first and second embodiments. This can make the print time for one material shorter than in the first and second embodiments.
A configuration and an image forming operation of an image forming apparatus according to a fourth embodiment are substantially identical to those adopted in the image forming apparatus of the first embodiment. Therefore, components having functions similar to those in the image forming apparatus of the first embodiment are denoted by the same reference numerals, and descriptions thereof are omitted.
In the first, second, and third embodiments, the optimal speed Vs between the time T1 and the time T2 differs according to the type of the transfer material and the surrounding environment of the transfer material. If the type and environment of the transfer material in marginless printing are known beforehand, the speed Vs can be controlled more properly. The optimal speed Vs differs according to the type and environment of the transfer material because the degree of bending of the transfer material varies in accordance with these conditions. For example, a thin transfer material greatly bends because its rigidity is low. In contrast, a thick transfer material does not greatly bend because its rigidity is high. Further, since the rigidity of the transfer material decreases in a high-temperature high-humidity environment, the transfer material bends greatly.
First, the type of the transfer material is detected with a media sensor 12 serving as a device for detecting the thickness of the transfer material, and the surrounding environment of the transfer material is detected with an environment sensor (not shown).
The environment sensor includes a temperature sensor and a humidity sensor, and is placed at an arbitrary position that is not affected by heat emitted and absorbed by the image forming apparatus itself. For example, a thermistor or a platinum temperature-measuring resistor is used as the temperature sensor, and a polymeric sensor, a metal oxide sensor, or an electrolytic sensor is used as the humidity sensor. In the environment sensor, the temperature sensor and the humidity sensor may be provided in a single unit or separately.
In the image forming apparatus of the fourth embodiment, the type and the surrounding environment of the transfer material are detected with the media sensor and the environment sensor during printing.
Then, the image forming apparatus determines optimum control over Vs between the time T1 and the time T2 on the basis of the detection result, and is fed back to the driving speed of the driving unit 17. More specifically, when the device for detecting the thickness of the transfer material detects that the transfer material is thick, control is performed so that the speed Vt3 of the transfer material at the time (T1+T2)/2 becomes closer to (Vt1+Vt2)/2 than when the device detects that the transfer material is thin. When it is detected that the transfer material is thin, control is performed so that Vt3 becomes closer to Vt2.
Optimum control over Vs is found beforehand in accordance with the combinations of the type and environment of the transfer material.
As described above, in the fourth embodiment, it is possible to more effectively prevent defective image forming caused in a plurality of types of transfer materials in a plurality of environments.
A configuration and an image forming operation of an image forming apparatus according to a fifth embodiment are substantially identical to those adopted in the image forming apparatus of the first embodiment. Therefore, components having functions similar to those in the image forming apparatus of the first embodiment are denoted by the same reference numerals, and descriptions thereof are omitted.
In the first to fourth embodiments, control is performed so that Vs<Vp at the time T1. This control can solve a problem that becomes more obvious when a margin is not provided at the leading edge of the transfer material in marginless printing. Therefore, when a margin is provided at the leading edge of the transfer material, it is not always necessary to perform control so that Vs<Vp. On the other hand, when the speed Vs at the time T1 is made higher during printing on the transfer material having a margin at the leading edge than during marginless printing, the time necessary for printing can be shortened.
In the fifth embodiment, the conveying speed of the transfer material from the time T1 to the time T2 is controlled in different modes between printing on a transfer material having a margin at the leading edge and printing on a transfer material having no margin even at a part of the leading edge, thus enhancing print time efficiency.
Then, the image forming apparatus performs printing according to the set mode. As described above, the fifth embodiment allows printing to be performed in a shorter time period when the user carries out printing on the transfer material having no margin at the leading edge and printing on a transfer material having a margin at the leading edge, than when printing is always performed in the marginless mode.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2008-115732 filed Apr. 25, 2008, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-115732 | Apr 2008 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5499086 | Matsuno et al. | Mar 1996 | A |
| 6356735 | Hozumi | Mar 2002 | B1 |
| 20050074267 | Demchock et al. | Apr 2005 | A1 |
| 20060251452 | Isozaki | Nov 2006 | A1 |
| 20070008397 | Maebashi | Jan 2007 | A1 |
| 20070201893 | Yamazaki | Aug 2007 | A1 |
| Number | Date | Country |
|---|---|---|
| 02282770 | Nov 1990 | JP |
| 04125676 | Apr 1992 | JP |
| 2004-45457 | Feb 2004 | JP |
| 2007-41582 | Feb 2007 | JP |
| 2007-52308 | Mar 2007 | JP |
| 2007-108562 | Apr 2007 | JP |
| 2008-046357 | Feb 2008 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20090269095 A1 | Oct 2009 | US |
